The present invention relates to a process for feeding transparency sheets and an apparatus useful therein.
One popular visual aid used in business and educational settings involves projecting the desired information from a transparent sheet onto a screen so that the information is simultaneously visible to numerous members of the audience. Typically, the transparency material contains the information which is then projected onto the screen by a projection apparatus such as an overhead projector. A reproduction apparatus such as a printer or electrographic copier is typically used to produce copies of original information on the transparency material.
However, transparency material has proven difficult to handle in typical reproduction apparatus because of certain inherent characteristics of transparency material. Typically, transparency material comprises non-fibrous flexible polymeric sheets which have a relatively high coefficient of friction and a high propensity to surface electrostatic charge build-up. As a result, transparency sheets tend to stick together due to the charge build-up and are hard to feed individually through reproduction apparatus.
A solution to the problem of feeding individual transparency sheets through reproduction apparatus has been to interleave plain paper separator sheets between adjacent transparency sheets as disclosed in U.S. Pat. No. 4,609,282. The transparency sheets and interleaved plain paper separator sheets are fed seriatim through the reproduction apparatus. The interleaving of the transparency sheets and the plain paper separator sheets facilitates sheet handling in the reproduction apparatus by reducing the effect of the high coefficient of friction of the transparency sheets and by preventing transparency sheets from sticking together due to surface charge buildup.
Even with the use of paper separator sheets, transparency sheets which have a soft coating thereon still present handling problems. Typical sheet or paper feed mechanisms for feeding the first paper sheet from a stack of such sheets commonly employ fixed feed wheels which move into engagement with the exposed sheet to cause the separation and feeding of the sheet usually by an initial buckling movement of the sheet. The sheet is then released from the stack so that the sheet may be fed through take-away rolls from the stack. The feed wheels usually remain at a fixed location in relation to the stack.
The problem which arises in feeding transparency sheets having a soft coating thereon from a stack is that the feed wheels easily damage the soft coating on the contacted transparency sheet and on the underlying transparency sheets by excessive localized pressure. This problem is especially prevalent upon start up, when sheet-to-sheet friction must be overcome and the feed wheels must get a grip on the transparency sheet to be moved. As such, the foregoing paper feed mechanisms are not useful in feeding transparency sheets having a soft coating thereon. The developer sheets described in commonly assigned U.S. Pat. No. 4,399,209 are an example of transparency sheets having a soft coating thereon which may be easily damaged by excessive localized pressure.
As such, a need exists in the art for a process for feeding transparency sheets and an apparatus useful therein wherein damage does not occur to the soft coating on the transparency sheets.